Acellular dermal matrix collagen responds to strain by intermolecular spacing contraction with fibril extension and rearrangement

Acellular dermal matrix (ADM) materials are used as scaffold materials in reconstructive surgery. The internal structural response of these materials in load-bearing clinical applications is not well understood. Bovine ADM is characterized by small-angle X-ray scattering while subjected to strain. Changes in collagen fibril orientation (O), degree of orientation as an orientation index (OI) (measured both edge-on and flat-on to the ADM), extension (from d-spacing changes) and changes to intermolecular spacing are measured as a result of the strain and stress in conjunction with mechanical measurements. As is already well established in similar systems, when strained, collagen fibrils in ADM can accommodate the strain by reorienting by up to 50 (as an average of all the fibrils). This reorientation corresponds to the OI increasing from 0.3 to 0.7. Here it is shown that concurrently, the intermolecular spacing between tropocollagen decreases by 10% from 15.8 to 14.3 angstrom, with the fibril diameter decreasing from 400 to 375 angstrom, and the individual fibrils extending by an average of 3.1% (D-spacing from 63.9 to 65.9 nm). ADM materials can withstand large strain and high stress due to the combined mechanisms of collagen reorientation, individual fibril extension, sliding and changes in the molecular packing density.